1. Field of the Invention
This invention relates to a magnetic disc apparatus provided with a shield member for reducing noise coupling to a magnetic head.
2. Description of Related Art
FIG. 1 is a sectional view showing a configuration of a conventional magnetic disc apparatus shown in, for example, Japanese Utility Model Application Laid-Open No. 60-173118 (1985). In FIG. 1 spindle motor 2 and an actuator 5 are fixed on a base 7 thereof. The spindle motor 2 drives to rotate recording/reproducing discs 12 wherein information is magnetic-recorded and a servo disc 11 having a servo surface wherein servo information, for positioning a recording/ reproducing head 4 which is described later, is magnetic-recorded. The actuator 5 drives a servo head 3 which reads the servo information from the servo disc 11 interlockingly with the recording/reproducing head 4 which reads information from the recording/reproducing disc 12.
At the position facing the periphery of the servo head 3, a shield plate 6 made of ferrite, permalloy or the like is provided, thereby preventing magnetism from entering the servo head 3 except for the servo information to be read.
In this conventional magnetic disc apparatus, the servo head 3 reads the positional information thereof by an electro-magnetic converting operation from the servo surface of the facing servo disc 11, thereby positioning the servo head 3 and the recording/reproducing head 4 interlocking with the servo head 3. But as noises such as electromagnetic wave and the like produced by the recording/reproducing head 4, except for the signals read from the servo surface of the servo disc 11, enters the servo head 3, this result in bad accuracy in positioning the servo head 3 and the recording/reproducing head 4. Therefore the noises coming to the servo head 3 are reduced by the shield plate 6 provided along the periphery of the servo disc 11, thereby improving the accuracy of positioning of the servo head 3 and the recording/reproducing head 4. The conventional shield plate 6 provided along the periphery of the servo disc 11 must approach to the periphery of the servo disc 11 as close as possible in order to reduce noises coming to the servo head 3. Moreover, it is necessary to provid the shield plate 6 and the servo disc 11 so as not to contact each other.
In the conventional magnetic disc apparatus, when the shield plate 6 faces the servo disc 11, usually a clearance gage is used or something like that to adjust the clearance, but there is a problem that working efficiency in installing the shield plate 6 is bad as the clearance between the servo disc 11 and the shield plate 6 is minute.